Editing Siméon Denis Poisson (section)

==== Electricity and magnetism ====

As the eighteenth century came to a close, human understanding of electrostatics approached maturity. [[Benjamin Franklin]] had already established the notion of electric charge and the [[Charge conservation|conservation of charge]]; [[Charles-Augustin de Coulomb]] had enunciated his [[Coulomb's law|inverse-square law of electrostatics]]. In 1777, [[Joseph-Louis Lagrange]] introduced the concept of a potential function that can be used to compute the gravitational force of an extended body. In 1812, Poisson adopted this idea and obtained the appropriate expression for electricity, which relates the potential function <math>V</math> to the electric charge density <math>\rho</math>.<ref name=":13">{{Cite book|last=Baigrie|first=Brian|title=Electricity and Magnetism: A Historical Perspective|publisher=Greenwood Press|year=2007|isbn=978-0-313-33358-3|location=United States of America|pages=47|chapter=Chapter 5: From Effluvia to Fluids}}</ref> Poisson's work on potential theory inspired [[George Green (mathematician)|George Green]]'s 1828 paper, ''[[An Essay on the Application of Mathematical Analysis to the Theories of Electricity and Magnetism]]''.

In 1820, [[Hans Christian Ørsted]] demonstrated that it was possible to deflect a magnetic needle by closing or opening an electric circuit nearby, resulting in a deluge of published papers attempting to explain the phenomenon. [[Ampère's force law|Ampère's law]] and the [[Biot–Savart law|Biot-Savart law]] were quickly deduced. The science of electromagnetism was born. Poisson was also investigating the phenomenon of magnetism at this time, though he insisted on treating electricity and magnetism as separate phenomena. He published two memoirs on magnetism in 1826.<ref name=":132">{{Cite book|last=Baigrie|first=Brian|title=Electricity and Magnetism: A Historical Perspective|publisher=Greenwood Press|year=2007|isbn=978-0-313-33358-3|location=United States of America|pages=72|chapter=Chapter 7: The Current and the Needle}}</ref> By the 1830s, a major research question in the study of electricity was whether or not electricity was a fluid or fluids distinct from matter, or something that simply acts on matter like gravity. Coulomb, Ampère, and Poisson thought that electricity was a fluid distinct from matter. In his experimental research, starting with electrolysis, Michael Faraday sought to show this was not the case. Electricity, Faraday believed, was a part of matter.<ref name=":02">{{Cite book|last=Baigrie|first=Brian|title=Electricity and Magnetism: A Historical Perspective|publisher=Greenwood Press|year=2007|isbn=978-0-313-33358-3|location=United States of America|pages=88|chapter=Chapter 8: Forces and Fields}}</ref>